Recently, a so-called "function-separated" type of electrophotographic photoreceptor has received wide attention. The light-sensitive layer of such photoreceptors comprises a charge generating layer which generates an electric charge when irradiated with light, and a charge transporting layer through which the electric charge generated by the charge generating layer can be efficiently injected and transferred. Amorphous silicon is generally used as the light-sensitive material in the preparation of the charge generating layer. An amorphous material produced by plasma chemical vapor deposition (CVD) method is generally used in the preparation of the charge transporting layer. The reason such electrophotographic photoreceptors have received such wide attention is due to the potentially dramatic improvements in chargeability and productivity which may be realized in conventional amorphous silicon based electrophotographic photoreceptors without compromising light sensitivity, high contrast and thermal stability, all of which are positive characteristics of amorphous silicon. There is also a potential for obtaining electrophotographic photoreceptors which have electrically stable repeating characteristics and long life. Accordingly, amorphous silicon based electrophotographic photoreceptors having a variety of different charge transporting layers have been proposed. In such function-separated type amorphous silicon-based electrophotographic photoreceptors, a charge transporting layer made of silicon oxide or amorphous carbon formed by the plasma CVD method as disclosed in, for example, U.S. Pat. No. 4,634,648 can be used.
As previously noted, in a conventional amorphous silicon based electrophotographic photoreceptor, chargeability may be enhanced with a reduction in dark decay by employing a layered structure having a charge transporting layer and a charge generating layer, wherein amorphous silicon is used in the preparation of the charge generating layer and a substance having a lower dielectric constant and a higher electrical resistance than amorphous silicon is used in the preparation of the charge transporting layer. The film forming speed of a film produced using the above plasma CVD method, however, is nearly equal to that of an amorphous film, and as a result, the layered structure is prone to complications. The complications include problems associated with increased potential of generating film defects, the problem of decline in productivity of the photoreceptor, and greatly increased production costs.